pkgbase: Move libprivatezstd from utilities to runtime

libarchive depends on it by default and tar uses libarchive.
So on a update :
1/ runtime contain tar
2/ runtime have libarchive in shlibs_required
3/ libarchive packages depends on utilities
4/ utilities depends on runtime
5/ kaboom

All users of libprivatezstd (libarchive related stuff and objcopy/ar)
are already in utilities.

Discussed with: bapt